1. Field of the Invention
The present invention generally relates to a method of manufacturing an orientation film, and specifically to a method of manufacturing a ceramic orientation film containing a piezoelectric ceramic. Furthermore, the present invention relates to a method of manufacturing a liquid discharge head (injection head) utilizing such a method of manufacturing an orientation film.
2. Description of a Related Art
A structure in which electrodes are formed on both sides of a piezoelectric material is utilized in various applications such as a piezoelectric actuator, a piezoelectric pump, an ink head of an inkjet printer and an ultrasonic transducer. In recent years, with the developments of MEMS (micro electro mechanical systems) related devices, elements having such structures have been microfabricated still further and packaged more densely. Accordingly, microfabrication and improvement in performance are desired for the piezoelectric material used there.
In the case where a piezoelectric ceramic such as PZT (Pb (lead) zirconate titanate) is used as a piezoelectric material, in order to improve the performance thereof, it is important to increase the degree of crystalline orientation in a piezoelectric material. Poling treatment of applying an electric field to the piezoelectric ceramic to align the orientation of electric duplexes in a crystal is performed such that the piezoelectric ceramic produces piezoelectric effect. This is because the higher the degree of crystalline orientation, the easier the poling, and therefore, higher piezoelectric performance is obtained.
By the way, there is epitaxial growth as a method of forming an orientation film including a single crystal film or a polycrystalline film in which crystals are oriented to some degree. The epitaxial growth refers to a technology by which an orientation film is grown on an orientation substrate of single crystal or the like, and vapor phase growth or liquid phase growth is normally used. Solid phase growth is not generally used because of slow growth rate, poor controllability and so on.
The fabrication of a single crystal film or orientation film by solid phase growth is disclosed in Ikesue, “A Review of Ceramic Materials for Optical Applications”, Laser Review (Special Issue “Development of Advanced Optical Materials for Laser”), The Laser Society of Japan, June 2002, Vol. 30, No. 6, pp. 290-296, and Japanese Patent Application Publications JP-P2003-267796A and JP-P2003-267800A. Ikesue teaches the principle of single-crystallization of a polycrystalline YIG ceramic by sintering the polycrystalline YIG ceramic in contact with seed crystals and the structural change from the polycrystalline YIG ceramic to a single crystal YIG ceramic (see FIGS. 21 and 22).
Further, JP-P2003-267796A discloses an oxide that can provide advantageous properties as a piezoelectric material and so on. The oxide is a single crystal or an orientation polycrystal having a perovskite structure containing components A, B and oxygen, and porosity of 0.01 volume percent to 8 volume percent.
Furthermore, JP-P2003-267800A discloses a high-quality oxide ion conductive crystalline material and a method of efficiently manufacturing the same. The oxide ion conductive crystalline material is substantially formed by orientation polycrystal expressed by ReX (MO4)6O1.5X-12 or single crystal with the number “n” per unit area (number/cm2) of crystal particles forming low-angle grain boundary where 0≦n≦102.
JP-P2003-267796A and JP-P2003-267800A disclose that, as a method of manufacturing a crystalline material, single crystallization or orientation of a polycrystalline sintered material with a seed crystal as a starting point by bringing the sintering material and the single crystal material (seed crystal) in contact and performing temperature control of heating the contact part and cooling ends of other parts (see FIG. 4 of JP-P2003-267796A and FIG. 4 of JP-P2003-267800A).
In the method of orienting a crystal by the solid phase growth, there have been four main problems as follows.
The first problem is that the polycrystalline ceramic material and the single crystal material are located in contact with each other. Here, it is important, for the single crystal material to capture fine particles of a ceramic for solid phase growth, that both are in close contact at the interface thereof. For the purpose, it is necessary to mirror-polish the single crystal face, bringing the polycrystalline ceramic material and the single crystal material in pressure contact, or filling the interface with a liquid phase material such that no gap is produced at the interface between them. However, such a step is added, the entire manufacturing process becomes complex and the apparatuses and equipment become complicated. Further, in the case where the area of the orientation film is increased, it is very difficult to uniformize the surfaces of the polycrystalline ceramic material and the single crystal material.
The second problem is that the ceramic sintered compact is used as a target to be oriented (polycrystalline ceramic material). In order to promote solid phase growth, it is more advantageous that the ceramic sintered compact is fabricated from micro particles. This is because the surface energy of particles is higher as the diameter is smaller, and the energy provided from the outside is lower. However, to fabricate a compact by using microparticles, binder is needed to maintain the shape. The binder comes out at the time of sintering, and thereby, pores are produced in the sintered compact. Accordingly, a dense film with particles in close contact with one another cannot be formed. Alternatively, sintering of the pressed compact of fine particles is conceivable. However, in this case, it is necessary to produce grain growth by heating the pressed compact afterwards. That is, the particle diameter has already been large at the time of fabrication of a ceramic sintered compact, and therefore, considerable energy is required to promote the solid phase growth from the condition.
The third problem is that the direction of orientation is controlled by temperature gradient. In order to orient the polycrystalline ceramic material, it is necessary to suppress the random grain growth and give priority to solid phase growth from the seed substrate (seed crystal) side. For the purpose, in the conventional technology, the temperature gradient is provided by heating the seed substrate side of the polycrystalline ceramic material and cooling end regions of the polycrystalline ceramic material. For example, in JP-P2003-267796A, the temperature gradient is set as 10° C./cm or more (p. 10). However, it is difficult to precisely control the temperature gradient, and the control of the temperature gradient is virtually impossible in the case where a film having a thickness of ten to several hundreds of micrometers is oriented.
The fourth problem is that the single crystal substrate is used as the starting point of solid phase growth. This is because the single crystal substrate is generally expensive and often restricted in area. Accordingly, the problem is a major issue in cost and technology when the device is put into practical use.